Publications from the Carcinogenic Potency Project

Ames, B. N., and Gold, L. S. The Causes and Prevention of
Cancer: The Role of Environment. In: The True State of the
Planet (ed. R. Bailey), Washington, D.C.: Free Press, 1995, pp.
141-175.

The idea that there is an epidemic of human cancer caused by
synthetic industrial chemicals is false.

If lung cancer (which is primarily due to smoking) is excluded,
cancer death rates are decreasing in the United States for all
other cancers combined. In addition, there is a steady rise in life
expectancy in the developed countries.

Pollution appears to account for less than 1 percent of human
cancer, yet public concern and resource allocation for chemical
pollution are very high, in good part because of the use of animal
cancer tests in cancer risk assessment.

About half of the chemicals tested, whether synthetic or
natural, are carcinogenic to rodents at the high doses tested in
rodents.

Linear extrapolation from near-toxic doses in rodents to
low-level exposure in humans has led to grossly exaggerated
mortality forecasts. Such extrapolations cannot be verified by
epidemiology. Furthermore, relying on such extrapolations for
synthetic chemicals while ignoring the enormous natural background
leads to an imbalanced perception of hazard and allocation of
resources.

Zero exposure to rodent carcinogens cannot be achieved. Low
levels of rodent carcinogens of natural origin are ubiquitous in
the environment. It is thus impossible to obtain conditions totally
free of exposure to rodent carcinogens or to background
radiation.

Risks compete with risks: society must distinguish between
significant and trivial risks. Regulating trivial risks or exposure
to substances erroneously inferred to cause cancer at low doses can
harm health by diverting resources from programs that could be
effective in protecting the health of the public.

Epidemiological evidence in humans is sufficient to identify
several broad categories of cancer causation for which the evidence
is strong and plausible. Since many of these are avoidable, it is
possible to reduce incidence rates of many types of cancer.

Tobacco is the most important global cause of cancer and is
preventable. Smoking contributes to about one-third of U.S. cancer,
about one-quarter of U.S. heart disease, and about 400,000
premature deaths per year in the United States.

The quarter of the population with the lowest dietary intake of
fruits and vegetables compared to the quarter with the highest
intake has roughly twice the cancer rate for most types of cancer
(lung, larynx, oral cavity, esophagus, stomach, colon and rectum,
bladder, pancreas, cervix, and ovary).

Decreases in physical activity and increases in smoking,
obesity, and recreational sun exposure have contributed to
increases in some cancers in the modern industrial world, whereas
improvements in hygiene have reduced other cancers related to
infection.

Chronic infections contribute to about one-third of the world's
cancer.